H
E
E
L
E
M
E
N
T
S
as DB is to BE,
so is GB to BF,
while,
as DB is to BE,
so is the parallelogram AB to the parallelogram FE, [VI.I]
and
as GB is to BF,
so is the parallelogram BC to the parallelogram FE, [VI.I]
therefore also,
as AB is to FE,
so is BC to FE; [V.11]
